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WO2013033015A1 - Microélectrodes de microchambre réactionnelle particulièrement pour interfaces neuronales et biologiques - Google Patents

Microélectrodes de microchambre réactionnelle particulièrement pour interfaces neuronales et biologiques Download PDF

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Publication number
WO2013033015A1
WO2013033015A1 PCT/US2012/052515 US2012052515W WO2013033015A1 WO 2013033015 A1 WO2013033015 A1 WO 2013033015A1 US 2012052515 W US2012052515 W US 2012052515W WO 2013033015 A1 WO2013033015 A1 WO 2013033015A1
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Prior art keywords
electrode
reaction chamber
transfer interface
electrochemical
chamber
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PCT/US2012/052515
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English (en)
Inventor
Bruce J. Gluckman
Balaji SHANMUGASUNDARAM
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The Penn State Research Foundation
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Publication of WO2013033015A1 publication Critical patent/WO2013033015A1/fr

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/02—Details
    • A61N1/04—Electrodes
    • A61N1/05—Electrodes for implantation or insertion into the body, e.g. heart electrode
    • A61N1/0551—Spinal or peripheral nerve electrodes
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6846—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive
    • A61B5/6867—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive specially adapted to be attached or implanted in a specific body part
    • A61B5/6877—Nerve

Definitions

  • This invention relates generally to micro-reaction chamber electrodes and more particularly to micro-reaction chamber electrodes for neural stimulation and recording. Description of the Prior Art
  • electrochemistry deals with the processes that take place at the interface between the electronic conductor (electrode surface) and the ionic conductor (electrolyte). Electrochemical activity and hence the impedance of a particular electrode is restricted to the active area that is in contact with the electrolyte. Generally, only those materials at the exposed surface take part in the electrochemical processes making the underlying bulk substrate less important in charge passing as long as the surface coating is intact and defect free. Electrolyte-based electrochemical reactants and reaction products can undergo subsequent reactions in the bulk that affect both charge passing efficacy as well as safety.
  • Neural recording and stimulation electrodes act as transducers that mediate signal transport between the ionic tissue environment and the solid-state electronic environment of the prosthetic device. Electrodes of smaller geometry are generally preferred to improve the spatial locality and to decrease the tissue damage resulting from insertion trauma. This, however, leads to increase in interfacial impedance and increase in the required charge transfer density for a given stimulation pulse. Since charge transfer takes place at the electrode-tissue interface by either Faradaic or capacitive mechanisms, the two-dimensional interfacial area, also called the electrochemical surface area (ESA), determines the electrochemical activity of the electrodes.
  • ESA electrochemical surface area
  • GSA geometric surface area
  • improving the surface roughness either by etching the surface or by depositing porous coatings on the surface such as Pt black, iridium oxide, or conductive polymer helps increase ESA and enhance electrochemical activity of the electrodes.
  • Modifying the surface morphology of the surface coating using micro and nanoscale templates to introduce pores has also resulted in significant increase in ESA.
  • the useful thickness of these coatings is limited by the chemical transport inside the pores and the possibility of fragile surface coatings, cracking or delaminating under mechanical stress in situ.
  • micro-reaction chamber electrode having impedance that can approach that of an ideal, geometrically defined electrode independent of capacitive or Faradic effects.
  • micro-reaction chamber electrode having minimal electrode impedance, maximum charge passing capacity, improved reversibility, decreased tissue damage, and a longer operational life.
  • the invention is a method for making highly localized low- impedance connections with an ionic conductive environment.
  • the method includes providing an electrode having a reaction chamber with an electrochemical transfer interface at least partially enclosed by an insulating layer and an open end terminating in an electrode interface in communication with the reaction chamber.
  • the method also includes connecting the electrode interface to tissue within the ionic conductive environment and spatially separating the electrode interface from the electrochemical transfer interface with the reaction chamber for increasing charge passing capacity and decreasing impedance.
  • the electrochemical transfer interface is distributed to be geometrically close to all positions in the bulk of the chamber and to have high surface to volume ratio.
  • the method also includes improving the electrochemical transfer capacity at the ETI by coating with one or more electroactive species such as iridium oxide and/or conductive polymer.
  • the ETI can be further extended through the chamber by growing it as a scaffold, for example by depositing through a polymer network such as sodium alginate hydrogel.
  • the reaction chamber can also be filled with a biocompatible dissolvable material to stiffen it during implantation.
  • the invention is a method for manufacture of micro- reaction chamber electrodes.
  • the method includes providing a mostly enclosed chamber volume terminating in an opening and having a high surface to volume ratio.
  • An electrochemical transfer interface is distributed throughout the chamber volume to maximize the surface area of the electrochemical transfer interface with respect to the chamber volume.
  • a conductor is also provided that is in charge carrying communication with the chamber volume via the electrochemical transfer interface.
  • the electrochemical transfer interface is coated with one or more electroactive species.
  • the electrochemical transfer interface may be extended into the chamber volume by one or more conductive threads or fibers, a conductive mesh or scaffolding, and by depositing through a polymer.
  • the invention is a micro-reaction chamber electrode.
  • the micro-reaction chamber electrode includes a mostly enclosed chamber volume terminating in an opening and having a high surface to volume ratio, an electrochemical transfer interface distributed throughout the chamber volume to maximize the surface area of the electrochemical transfer interface with respect to the chamber volume, and a conductor in charge carrying communication with the chamber volume via the electrochemical transfer interface.
  • the micro-reaction chamber electrode includes an electroactive species covering the inner surface of the chamber volume to increase its charge passing capacity.
  • a conductor may be configured to extend into the chamber volume to extend the electrochemical transfer interface.
  • Figs. l(a)-(c) are exemplary illustrations of various embodiments for different reaction chamber electrochemical transfer interface geometries of the present invention.
  • Figs. 2(a)-(c) are exemplary illustrations of a fabrication process for microwire based micro-reaction chamber electrodes of the present invention.
  • Figs. 3(a)-(c) are SEM images of each stage represented in the fabrication process shown in Figs. 2(a)-(c).
  • Figs. 4(a)-(c) are additional exemplary illustrations of the fabrication process for microwire based micro-reaction chamber electrodes shown in Figs. 2(a)-(c).
  • Figs 5(a)-(c) are additional exemplary illustrations of the fabrication process for microwire based micro-reaction chamber electrodes shown in Figs. 2(a)-(c) and 3(a)-(c).
  • Fig. 6 is an illustration of an array of micro-reaction chamber electrodes fabricated in parallel according to one aspect of the present invention.
  • Fig. 7 is another illustration of an array of micro-reaction chamber electrodes fabricated in a base material according to one embodiment of the present invention.
  • Fig. 8 is another illustration of an array of micro-reaction chamber electrode fabricated as protruding from a base material according to another embodiment of the present invention.
  • Fig. 9(a) is a plot of current versus voltage for a solid-planar (SP1) electrode shown as a function of the various stages of deposition.
  • Fig. 9(b) is a plot of current versus voltage for a microwire micro-reaction chamber electrode of the present invention shown as a function of the various stages of deposition.
  • Fig. 9(c) is a plot of charge storage capacity (CSC) as a function of the various stages of deposition comparing the microwire micro-reaction chamber electrode of the present invention to the SP1 electrode.
  • Fig. 10(a) is a plot of current versus voltage for as a function of increasing dissolution time comparing the microwire micro-reaction chamber electrode of the present invention to the SP1 electrode coated with EIROF (iridium oxide).
  • Fig. 10(b) is a plot of charge storage capacity (CSC) as a function of increasing dissolution time comparing the microwire micro-reaction chamber electrode of the present invention to the SP1 electrode.
  • CSC charge storage capacity
  • Fig. 11 shows a pair of plots for impedance magnitude (upper) and phase (lower) versus frequency for embodiments of various electrodes of the present invention.
  • Fig. 12 is a plot of voltage transient and current waveform versus time for a microwire micro-reaction chamber electrode in phosphate buffered saline (PBS) during pulse stimulation, with definition of the anodic, cathodic, and base electrode polarization voltages E ma , E mc , Eb ase used to determine maximal safe stimulation limits.
  • PBS phosphate buffered saline
  • Figs. 13(a)-(c) are plots of electrode polarization voltages versus pulse amplitude for an electrodeposited iridium oxide (EIROF) SP1 electrode shown in Fig. 13(a) and an electrodeposited iridium oxide (EIROF) micro-reaction chamber electrode at 5 minutes electrodissolution shown in Fig. 13(b) and 10 minutes electrodissolution shown in Fig. 13(c).
  • EIROF electrodeposited iridium oxide
  • EIROF electrodeposited iridium oxide
  • Figs. l(a)-(c), 2(a)-(c), and 4(a)-(c) illustrate exemplary embodiments of micro- reaction chambers ⁇ RC) of the present invention in which a volume within the electrode back plane is used to confine and sequester the electrochemical reactions that are involved in charge passage.
  • the connection from the ⁇ RC to the tissue is an opening that replaces the geometric surface of a classical electrode.
  • the area of the electrode back plane replaces the two-dimensional ESA of the solid-planar (SP1) electrode for charge exchange, offering much higher electroactivity for the given GSA.
  • SP1 solid-planar
  • electrochemical reaction products within the micro-chamber help enhance the reversibility of the charge transfer reactions and improving charge transfer safety. Further when implanted in the neural tissue, the reactive coatings are protected from the insertion related damages and tissue inflammatory reactions as they are encapsulated within the reaction- chambers.
  • Figs. l(a)-(c), 2(a)-(c), and 4(a)-(c) illustrate basic designs of ⁇ RC electrodes according to embodiments contemplated by the present invention.
  • the complete volume of the hollow region within the inner diameter (d) and length (1) is defined as the micro- reaction chamber (see Fig. 1(a)).
  • the outer insulation restricts the electrical axis only through the opening at the tip and helps maintain the same geometric surface area (GSA) as that of other reference or solid-planar electrodes.
  • GSA geometric surface area
  • the ⁇ -C electrode achieves (l+4(l)/(d)) times larger effective GSA (EGSA) than SP1 electrodes.
  • ETI reaction chamber electrochemical transfer interface
  • Figs. l(a)-(c) provide illustrations of varying ETI geometries, the present invention contemplates other ETI geometries. For example, any geometry that maximizes the surface area of the ETI relative to the volume of the chamber is desirable.
  • FIG. 2(a)-(c) A fabrication process for preparing ⁇ electrodes according to a general aspect of the present invention is shown in Figs. 2(a)-(c) and Figs. 4(a)-(c).
  • a base stock of wire comprised of an active core, coated with a noble metal coating and insulated on the outside or cleaved on one end may be used (see Figs. 2(a)).
  • An SEM image of a microwire corresponding to the schematics shown in Fig. 2(a) is shown in Fig. 3(a).
  • a dissolution process is used to dissolve the active core to form a reaction chamber as shown in Fig. 2(b).
  • electrodissolution is shown in Fig. 3(b).
  • the depth of the reaction chamber may be controlled by adjusting the duration of the electrodissolution process.
  • the active core within the reaction chamber is encapsulated with a noble metal as shown in Fig. 2(c).
  • the walls of the chamber which form the electrochemical transfer interface (ETI) may be coated with an electroactive coating as shown in Fig. 4(b) to improve charge passage from the solid-state electronic conductor to the electrolyte solution.
  • An SEM image of the electroactive coating is shown in Fig. 3(c).
  • the reaction chamber can also then be filled and/or coated with a polymer hydrogel to improve biocompatibility as shown in Fig.
  • a dissolvable coating to provide structural support during insertion.
  • filling the tube with the hydrogel as shown by illustration in Figs. 4(c) & 5(b), will provide stiffness for insertion through a jelly-like electrochemical environment, such as brain tissue, and provide a conductive channel for ionic transport between an electrode and electrolyte.
  • Electroactive materials e.g., conductive polymer/iridium oxide
  • the electroactive scaffold shown in Fig. 5(c) is deposited to act as the electrochemical transfer interface (ETI).
  • the inner surface of the conductive tube can be coated with an electroactive coating or film, such as iridium oxide or conductive polymers as discussed above and further shown by illustration in Fig. 4(b).
  • the inner surface of the conductive tube may also be filled with hydrogels to form the scheme illustrated in Fig. 4(c).
  • the reaction chamber ETI may also be deposited with a multilayer stack of electroactive species, for example a combination of electrodeposited iridium oxide and conductive polymer, which increases the electroactivity of the electrode as discussed above.
  • the present invention also contemplates the parallel fabrication of ⁇ -C electrodes configured as microwire arrays, such as the exemplary illustration provided in Fig. 6.
  • each microwire includes a mostly enclosed volume (i.e., micro-reaction chamber), a noble metal conductor and an ETI.
  • the microwire also includes an active core.
  • the array of microwires is brought into contact with an ionic environment, such as tissue.
  • Figs. 7-8 illustrate other exemplary embodiments of the micro-reaction chamber electrode of the present invention.
  • the micro- reaction chamber electrode can be fabricated as part of a larger structure device using current or newer fabrication or micro fabrication processes.
  • the micro- reaction chamber electrode could be fabricated as part of an array made with solid backings which contain electrical connections and/or active electronics formed from or on silicone, parylene, or polyimide.
  • micro-electrode arrays can then be formed as single elements or arrays from wells or tubes that are fabricated into the back plane, and have an opening to the ionic solution.
  • the micro- electrode arrays could take the form of tubes that are insulated from the outside, except at the physical opening at the terminal end of the reaction chamber that establishes the electro-connection with the ionic system of interest.
  • the wells or tubes constitute the reaction chamber. Charge is electrochemically exchanged into the chamber through an ETI, which is formed from a solid-state conductive element.
  • the conductive element forming the ETI could be gold, or another non-reactive (or minimally reactive) metal or nonmetal conductor, including platinum, iridium, conductive polymer, conductive composite materials, carbon fiber, carbon nanotubes (CNT), etc.
  • the geometry of the ETI may be a tube formed from the inside walls of the chamber. Alternately, the ETI can be constructed from single or multiple conductive fibers within the chamber (see Fig. 1(b)) or a structured or unstructured mesh of conductor within the chamber (see Fig. 1(c)).
  • Embodiments of the present invention are further defined in the following non- limiting examples and in B. Shanmugasundaram and B.J. Gluckman, "Micro-reaction chamber electrodes for neural stimulation and recording” Proc. IEEE Eng. Med Biol. Soc. 2011, pp. 656-659 which is incorporated by reference herein in its entirety. It should be understood that this example, while indicating a certain embodiment of the invention, is given by way of illustration only. From the above discussion and this example, one skilled in the art can ascertain the essential characteristics of the invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the embodiments in the invention to adapt it to various usages and conditions. Thus, various modifications of the embodiments of the invention, in addition to those shown and described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.
  • micro-reaction chamber electrodes were prepared from 50 ⁇ diameter 316L stainless steel microwires plated with 1 ⁇ thick gold and insulated with polyimide (Supplier: California Fire Wire Company, Grover Beach, CA, USA).
  • the tip of the electrode is cut flat using a razor blade, creating a terminal end generally perpendicular to the electrode.
  • the schematic of the steps involved in the fabrication of the micro wire based ⁇ 3 ⁇ 4£ electrode are shown in Figs. 2(a)-(c), 3(a)- (c), and 4(a)-(c).
  • Selective electrochemical dissolution of 316L leaves behind a hollow, tubular region that is insulated from the outside.
  • the exposed 316L is electroplated with gold according to one embodiment of the invention. Then, this hollow region may be deposited in one aspect of the present invention with multilayered coatings that contain stacks of electrodeposited iridium oxide (EIROF) and electropolymerized poly(3,4- ethylenedioxythiophene) (PEDOT) conductive polymer.
  • EIROF electrodeposited iridium oxide
  • PEDOT electropolymerized poly(3,4- ethylenedioxythiophene)
  • Selective electrochemical dissolution of 316L stainless steel from the gold plated microwire was accomplished in part using a protocol identified as the ASTM B912 standard.
  • a gold plated electrode is used in fabrication of the micro-reaction chamber electrode, the present invention contemplates that other conductive elements may be used in place of the gold, such as another non-reactive (or minimally reactive) metal or nonmetal conductor, including platinum, iridium, conductive polymer, conductive composite materials, carbon fiber, carbon nanotubes (CNT), etc.
  • a 1 : 1 mixture (v/v) of concentrated sulphuric acid-phosphoric acid electrolyte heated to 75°C was used for selective electrochemical dissolution of the 316L stainless steel from the electrode.
  • Electrodeposition of Electroactive Coatings on the Electrochemical Transfer Interface Figs. l(a)-(c), 2(a)-(c), 3(a)-(c) and 4(a)-(c) illustrate the electrodeposition of iridium oxide.
  • the iridium oxide electrodeposition solution (Solution A) may be prepared by dissolving 4 mM IrCl 4 hydrate in 40 mM oxalic acid solution.
  • the pH of this solution may be adjusted to 10.4 by slowly adding 3 M K 2 CO 3 buffer solution.
  • the color of the solution changes from dark purple to pale green.
  • the solution is allowed to sit quiescently in the dark for a minimum of one week at room temperature before electrodeposition.
  • the oxidation state of Ir in the oxalate complex attains equilibrium during this period.
  • Electrodeposition of the iridium oxide layer was carried out using a two-electrode cell potentiostat using a large surface area AgCl pellet as a counter electrode.
  • a PEDOT:PSS electropolymerization solution (Solution B) may be prepared by dissolving 0.01 M of EDOT monomer in a 0.1 M poly(sodium 4-styrene sulfonate) solution. Mixing the solution overnight ensure complete dissolution of the EDOT monomer.
  • the PEDOT:PSS electropolymerization may be performed using a three- electrode cell potentiostat.
  • Stack coatings on SP1 electrode and ⁇ £ electrode substrates may be applied in three states.
  • stage I using Solution A, iridium oxide is electrodeposited by applying a combination of potential cycling with 50 triangular waveforms between limits of 0.0 V and 0.55 V at 50 mV/s sweep rate followed by 1000 rectangular potential pulses between the same voltage limits with 0.5 s width in each limit between the substrate and a large area AgCl pellet at room temperature.
  • stage II for example, the PEDOT:PSS conductive polymers potentiostatically electropolymerized from Solution B, at 0.9 V vs. SCE reference in a three-electrode cell for 60 seconds. A large area Pt pellet may serve as the counter electrode in this case.
  • the top layer of iridium oxide is electrodeposited from Solution A in state III, by applying 1800 rectangular potential pulses between 0.0 V and 0.55 V limits with 0.5 s width in each limit against a large area AgCl pellet.
  • the morphology of the electrodes was imaged in an LEO 1530 field emission scanning electron microscope (FESEM).
  • FESEM field emission scanning electron microscope
  • the in vitro electrochemical characterizations were performed in a phosphate buffered saline solution.
  • Electrochemical Impedance Spectroscopy (EIS) was recorded using an Autolab PGSTAT-12.
  • An AC sinusoidal signal of 10 mV rms was used to record the impedance over a frequency range of 0.1-100000 Hz.
  • the test electrodes are connected as working electrodes and a large area Pt foil served as a counter electrode.
  • the saturated calomel electrodes were used as reference electrodes.
  • CSC charge storage capacities
  • anodal-first biphasic charge- balanced current pulses are applied with symmetric cathodal and anodal pulse widths of 0.2 ms/phase and an interphase delay of 0.1 ms at 50Hz in PBS using a constant-current stimulator between the test electrode and a large surface area 316L stainless steel current- return electrode and monitor the potential transient against a Ag/AgCl reference electrode.
  • the interphase delay of 0.1 ms is introduced to disregard the access voltage resulting from the solution resistance.
  • the potential measured at the starting of the interphase delay (E ma ) is a measure of the electrode polarization required to support the charge injection in the anodic leading phase.
  • E mc is a measure of electrode polarization in the cathodic direction.
  • the amount of charge injected in the leading phase of the pulse is the product of pulse amplitude and pulse width.
  • Qi n j is the maximum charge density (charge injected divided by the GSA of the electrode) injected before either E ma crosses the positive threshold of 0.8 V or E mc crosses the negative threshold of -0.6 V.
  • Figs. 13 (a)-(c) are the electrode polarizations for increasing pulse amplitude for EIROF coated SP1 electrode (see Fig. 13(a)) and ⁇ -C electrodes at 5 minute (see Fig. 13(b)) and 10 minute (see Fig. 13(c)) electrodissolution durations.
  • the charge limits corresponding to the polarization crossing the thresholds of water electrolysis window for each electrode is marked by the vertical dashed line.
  • the polarization crosses the -0.6 V limit for pulse amplitude of 0.11 mA.
  • the Qi nj limit for this electrode is 1.02 mC/cm2.
  • the limit for the micro- reaction chamber electrode for an etch duration of 5 minutes is 2.04 mC/cm and for the substrate with etch duration of 10 min is 3.06 mC/cm .
  • Electrodissolution in hot sulphuric-phosphoric acid mixture resulted in selective dissolution of the active 316L stainless steel leaving behind a hollow noble metal (gold) tube that is insulated with polyimide from the outside.
  • gold gold
  • the depth of the micro-reaction chamber can be controlled. Selection of proper insulation material is critical, as the insulation material must be able to survive exposure to both the neural tissue environment and the electrodissolution solutions.
  • Polyimide insulation is used for example in an exemplary aspect of the present invention.
  • Figs. 9(a)-(c) Charge Storage capacity as measured by cyclic voltammetry for microwire electrodes formed from 50 ⁇ diameter wire stock are shown in Figs. 9(a)-(c).
  • the cyclic voltammograms are shown as a function of the deposition stage for a three layer stack electroactive coatings. Specifically, in Fig. 9(a) and Fig. 9(b) the average current vs.
  • the ⁇ £ electrodes (without coatings) demonstrated one order of magnitude lower impedance as compared to that of the bare reference SPl electrodes for frequencies below 10 kHz.
  • the addition of three-layered stack coatings significantly reduced the impedance of both the reference SPl and ⁇ -C electrodes of the present invention.
  • phase behavior for the coated reference SPl is far less clear in interpretation.
  • Charge passing capacity is also a function of the volume of the reaction chamber. Chamber depth can be controlled in the microwire fabrication through for example the dissolution time, with longer dissolution time providing a deeper well and larger volume. Cyclic Voltammograms and CSCs for microwire electrodes with different dissolution times are presented in Figs. 10(a)-(b), with zero dissolution time corresponding to SPl electrodes. As shown, CSC increases with chamber depth. It should be noted that deposition protocol of electroactive materials, such as the iridium oxide used here, needs to be altered for deeper chambers to ensure uniform coating on the electrochemical transfer interface (ETI).
  • ETI electrochemical transfer interface
  • Micro-reaction chamber electrodes with improved in vitro electrochemical characteristics are prepared from microwire electrodes.
  • the coated microwire ⁇ -C showed about three orders of magnitude higher charge storage capacity than a bare solid- planar (SPl) electrode.
  • SPl bare solid- planar
  • the ⁇ £ electrodes can pass significantly higher amount of charge.
  • ⁇ -C electrodes with smaller GSA can replace any counterpart with a higher GSA.
  • ⁇ -C electrodes can help reduce the tissue trauma and increase the selectivity.
  • Micro-reaction chamber electrodes also provide greatly improved charge injection under conditions used for pulse stimulation. Electrode polarization during pulse stimulation with anodic first biphasic charge-balanced symmetric pulses 0.2 ms/phase 0.1 ms inter-phase interval applied at 50 pulses/s is presented in Figs. 10(a)-(b) for EIROF coated micro wire electrodes with three different ⁇ dissolution times. SP1 micro wire electrodes (at zero dissolution time) reach unsafe electrode polarization at the lowest stimulation amplitude. The creation of a micro-reaction chamber greatly improves on this performance, with nearly a threefold improvement over the bare electrode being observed within the 10 minute dissolution time. As shown, longer duration etching increases the charge storage capacity of the electrodes. Increasing the duration of electrodissolution results in deeper micro-reaction chambers. This provides higher surface area for the electrochemical transfer interface (ETI) for a given GSA and hence supports higher charge transfer.
  • EI electrochemical transfer interface
  • the ability to excite action potential from pulse stimulation is limited by the current amplitude of the applied pulse, which is in turn limited by the safety.
  • improved charge injection capacity under pulse stimulation increases the ability to interact with brain.
  • microwire based ⁇ The developed methodology for fabricating microwire based ⁇ can directly be extended to batch production in multi-electrode bundles.
  • the utility of the present invention is not limited to electrical measurement and stimulation in biological tissue.
  • the utility of the present invention is generally for making highly localized low-impedance connections with ionic conductive systems or features within an ionic environment, where one would like to either or measure potentials and/or pass current from a geometrically localized position. Such examples might be for measurement of electrochemical potentials or monitoring chemical species or applying current at localized positions within a larger reaction chamber. The advantages are the same in these cases as with interfacing with biological tissue.
  • the present invention contemplates the use of other like materials exhibiting like characteristics.
  • the conductive tube material is generally a material that has lower chemical reactivity in the given electrolyte than the active core metal.
  • the conductive tube material possesses a good biocompatibility for use as a neuroelectrode.
  • the conductive tube material is also generally capable of withstanding the harsh electropolishing and neurotissue environment.
  • Examples of conductive tubing or conductive element to form the tube could be gold, or another non- reactive (or minimally reactive) metal or non-metal conductor, including platinum, iridium, conductive polymer, conductive composite materials, carbon fiber, carbon nanotubes (CNT), etc.
  • the present invention also contemplates various materials for uses as an insulator or an insulating layer for the micro-reaction chamber microelectrode. In general, the insulation should bond well to the conductive tube material and have a high dielectric constant. The insulation should withstand harsh electropolishing and be compatible with neurotissue. In one exemplary embodiment of the present invention, polyimide is used as the insulating layer. Other insulators, such as parylene, may be used as an insulator.
  • the active core metal is stainless steel.
  • Other active core materials are contemplated.
  • the core material provides rigidity to the whole structure.
  • the core material is preferably anodic to the tube material so it will undergo preferential dissolution in the sulphuric-phosphoric acid mixture.
  • the active core material also possesses good corrosion resistance and biocompatibility.
  • the electroactive coatings include iridium oxide and conductive polymers. Other coatings are also contemplated.
  • the electroactive coating should be biocompatible and stable, and capable of passing more charge across the electrode-tissue interface. The electrochemical changes the electroactive coating undergoes when applying an electrical signal should also be reversible.
  • the polymer network such as a hydrogel
  • the polymer network should be biocompatible and stable in brain tissue environment or in another ionic environment.
  • the present invention contemplates sodium alginate hydrogel as one possible polymer network for providing sufficient porosity for ionic solution/fluid to flow or diffuse through the polymer network.
  • Other polymer networks are also contemplated herein.
  • the polymer network such as hydrogel, serves as a mechanical buffer between the soft tissue and the hard/stiff electrode.
  • the polymer network can serve as a structure or scaffold for the growth of conductive polymers or other materials added to increase electrochemical charge transfer. The result is a highly porous - or maybe skeletal - conductive structure configured in combination with a micro- reaction chamber.

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Abstract

La présente invention concerne des électrodes biocompatibles dotées d'une surface géométrique plus petite améliorant la sélectivité des applications d'enregistrement et de stimulation neuronaux. Un volume au sein de la face arrière de l'électrode d'une microchambre réactionnelle est utilisé pour confiner et séquestrer une réaction électrochimique utilisée pour un passage de charge. L'électrode de microchambre réactionnelle diminue l'impédance et améliore la capacité de stockage de charge sans modifier la géométrie du site actif.
PCT/US2012/052515 2011-08-28 2012-08-27 Microélectrodes de microchambre réactionnelle particulièrement pour interfaces neuronales et biologiques WO2013033015A1 (fr)

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